Please refer to FIG. 1 and FIG. 2, which a top view and a cross-sectional view showing a conventional blower impeller. The impeller includes a hub 40 and an impeller 41. The hub 40 has a spindle disposed centrally therein and is connected with the impeller 41 by several swirl-like ribs 42.
The impeller 41 contains several blades 411, a pressure-retaining ring 43 and a top connection ring 44, in which the outer edge on the top side of each blade 411 is connected with a top connection ring 44, and a pressure-retaining ring 43 is disposed on the bottom side of the blades 411 to fully cover the bottom portion of the blades, has a fixed thickness and is a disc-like part that can prevent air flow from being released from the bottom portion of the blades, so as to enhance the function of static pressure and reinforce the strength of the blades as well.
Please refer to FIG. 2, which is a cross-sectional view showing the operation when a conventional blower impeller is disposed in a housing. External air (as indicated by arrowhead) enters from a spatial range surrounded by the periphery of the hub 40 and the inner end portion of the blade to form an axial flow. When the impeller rotates, the axial flow entering from the spatial range surrounded by the periphery of the hub 40 and the inner end point of the blade into the impeller is converted into a radial flow due to a centrifugal force resulting from the spinning effect and is stirred up by the blades 411 to exhaust. An external air flow entering from a place right above the blade 411 forms an axial air flow directly flowing down to the pressure-retaining ring 43. The pressure-retaining ring 43 can block air to prevent air from being directly released from the bottom portion of the blades 411 and from lacking of air pressure due to the air pressure release. Therefore, the pressure-retaining ring 43 can increase air pressure and air volume while the impeller is driving.
Whereas, when passing through the blades 411, the radial flow formed by the centrifugal force will confront with the axial flow entering from the place right above the blade 411 so that collision of the air flows from two different flow directions will happen. Such collision leads to the occurrence of turbulence which results in the instability of air-flowing direction of the impeller.
In view of the foregoing concern, to overcome the aforementioned drawbacks, the present invention provides an impeller having a plurality of pressure relief holes capable of reducing the occurrence of turbulence and further providing the function of increasing air pressure and air volume.